SELECT     MAX(DATEDIFF(year, dbo.Employees.BirthDate, GETUTCDATE ()) ) 'greatest age', 
           MIN(DATEDIFF(year, dbo.Employees.BirthDate, GETUTCDATE ())) 'smallest age',
           AVG( DATEDIFF(year, dbo.Employees.BirthDate, GETUTCDATE ())) 'average age'
FROM       [Northwind].[dbo].[Employees] 
WHERE City='London'



 select DATEDIFF(year, dbo.Employees.BirthDate, GETUTCDATE ())
 FROM       [Northwind].[dbo].[Employees] 
WHERE City='London'